The present invention pertains to a process for joining components and assembly units of rail-borne vehicles.
Attempts have been increasingly made in manufacturing rail-borne vehicles to replace complex, stress-transmitting nonpositive and positive welded, riveted or screw connections with equivalent bonded connections. It has been known that bonded assembly units can achieve fatigue strengths specific of rail-borne vehicles with one-component or two-component polyurethane adhesives. One essential drawback of the use of such adhesives is that they require a certain gap width and need defined curing times before they reach a strength that allows handling, transportation and further machining of the assembly units, so that long fixing times with maintenance of a defined joining pressure must be maintained. Adhesives that make possible very short fixing times, such as acrylate adhesives, are, in contrast, frequently not resistant to aging and cannot ensure uniform fatigue strength properties.
To reduce the technological fixing times, it is proposed in DE 35 25 830 A1 that thin-walled body parts be joined by bonding by applying a more slowly curing and permanently load-bearing principal adhesive (e.g., a strip-like strand of a two-component adhesive) to one of the elements, by subsequently bringing together the elements to be joined and joining them under pressure and subsequently applying a quick-curing adhesive (e.g., a quick-curing one-component adhesive based on cyanoacryl) in areas of the bonded joint adjacent to the principal adhesive under joining pressure between the elements, wherein the quick-curing adhesive can assume the function of the prior-art bonding device after a relatively short time. To make it possible to maintain the necessary bonding gap widths, the components to be joined are shaped in a trough-shaped or groove-shaped manner in the area of the bonded joint. In the first exemplary embodiment, the quick-curing adhesive is injected between the components through openings in one of the components. The device intended for the application of the quick-curing adhesive and the application of the necessary joining pressure is complicated; one device is necessary for each site of application or a subsequent positioning of the elements in the case of the application example described. In the second case of application, the quick-curing adhesive is applied, e.g., in troughs of one of the elements by means of glass ampules or film bags, which are destroyed during the joining process. This process cannot be used for cases of application in which components with manufacturing tolerances in relation to one another are to be joined without specially shaped bonded joints with defined layer thicknesses. Such an assembly unit obtains a decorative surface only by a subsequent equalization of the surface and surface coating.
To maintain certain bonded joint gaps, the bonding process described in EP 0 433 513 A1 provides for calibrated limiting and spacing elements in the edge area or within the bonded joint.
In DD 241 768 A1, defined points or areas of the bonded joint are provided with material elevations or applications of the same substance.
If parts with manufacturing tolerances must be joined, the latter two methods fail; moreover, in the case of a given surface, such inclusions interrupting the bonded joint and the means rigidly spacing the components to be joined from one another may reduce the bonding strength that can be theoretically reached with the given adhesive or may make it compulsory to provide much larger joining surfaces than theoretically necessary.
Moreover, the use of adhesives frequently leads to the problem that adhesive residues spreading beyond the surface area intended as a joining surface can be removed with a great mechanical or chemical effort only, which may lead to damage to the component. For example, adhesive tapes are therefore usually used as an edge limitation of the joining surfaces, and these adhesive tapes can then be separated from the surface. Their application and subsequent removal require a great effort; they usually must be disposed of as special waste.
The primary object of the present invention is to provide a novel process for joining assembly units of rail-borne vehicles by means of bonding, in which the application of an adhesive, which ensures fatigue strength and requires a relatively long curing time, is combined with the application of an adhesive that ensures a strength sufficient for handling in a short time, wherein complicated shaping of the bonded joints as well as great efforts in terms of devices are to be avoided, manufacturing tolerances between the components to be joined are to be equalized and defined minimum bonded joint gaps between the components are to be maintained, without strength-reducing disturbances occurring within the bonded joint. Another object of the present invention is to make it possible to limit the wetting of the surfaces of components with adhesive to selected joining surfaces and to avoid the subsequent removal of a covering edge limitation and its disposal as special waste.
According to the invention, a process is provided for joining components of rail-borne vehicles by bonding, in which a preformed first component is joined to a shape-adapted second component by means of the two-dimensionally separate application of adhesives with different reaction characteristics until a strength sufficient for handling is reached. The process includes bringing a first component into the position for joining and fixing in the form of use in the usual manner. A first adhesive layer having the property of being quick-bonding and maintaining a defined joining layer thickness is applied to selected and two-dimensionally limited first joining surfaces of the first component and/or of the second component. A defined amount of a second adhesive layer having the property of curing more slowly and flowing slowly during joining, but being flowable and capable of wetting, is applied to selected second joining surfaces of the first component and/or of the second component. The two components to be joined are positioned in the desired three-dimensional arrangement in relation to one another, are brought close to one another and are joined to one another under the effect of a joining pressure applied in the area of said selected first joining surfaces. The first adhesive layer connects the first component to the second component in the area of the first joining surfaces at a joining space predetermined by the defined joining layer thickness of the first adhesive layer with such a first joining strength that removal and moving of the pre-joined assembly unit is possible after the joining process without any change in the shape and position of the components. The second adhesive layer, whose amount as well as flowability and wetting ability are such that the first adhesive layer applied can contact the other component in the area of the joining surfaces, fills out the joining space left between the first and second components in the area of the second joining surfaces the assembly unit subsequently remains in its joined position or is brought into a resting position or is included in the further technological process, where a second joining strength brought about by the curing of the second adhesive layer is reached.
According to another aspect of the invention, another process for joining components of rail-borne vehicles is provided. The first component is brought into the position for joining and fixed in the form of use in the usual manner. An adhesive layer, having the property of being quick-bonding and maintaining a defined joining layer thickness during joining, is applied to said selected and two-dimensionally limited first joining surfaces of the first component and/or of the second component. The two components to be joined are positioned in the desired three-dimensional arrangement in relation to one another, are brought close to one another and are joined together under the effect of a joining pressure applied in the area of the said selected first joining surfaces. The first adhesive layer connects the first component in the area of the joining surfaces at a joining space predetermined by the defined joining layer thickness of the first adhesive layer with such a first joining strength that removal and moving of the pre-joined assembly unit is possible without any change in the shape and position of the components in relation to one another. A defined amount of a second adhesive layer having the required flowability and wetting ability is introduced into the joining space left between the first and second components in the area of selected second joining surfaces. The assembly unit subsequently remains in its joined position or is brought into a resting position or is included in the further technological process, where a second joining strength brought about by the curing of the second adhesive layer is reached.
With each of the above processes, the first joining surfaces provided may be selected such that at least part of the second joining surfaces provided is limited by parts of the first adhesive layer and undesired wetting of additional surfaces of the component by the adhesive of the said second adhesive layer is prevented.
A contact-adhesive adhesive may be used for the first adhesive layer. Intrinsically dimensionally stable adhesive bodies may be used for the first adhesive layer. A reactive adhesive may be used for the second adhesive layer. An adhesive that has the same elasticity as or a higher elasticity than the adhesive for the second adhesive layer after the final curing of this second adhesive layer may be used for the first adhesive layer.
A plurality of first and second joining surfaces may be arranged alternatingly adjacent to one another in a joined connection such that the joined connection acquires increased safety against failure. Differences in the shape and size of the components to be joined (e.g. a side wall sheet metal section and a profile section) may be equalized by varying the thickness of one or both said adhesive layers.
At least two adhesives with different viscosities and/or with different properties in the cured state may be applied two-dimensionally next to each other as a second adhesive layer in the area of the said second joining surfaces.
The following advantageous effects are achieved with the present invention compared with the state of the art:
Compared with prior-art bonding processes, a way has been found for preparing assembly units of rail-borne vehicles by bonding by means of more slowly curing one-component or two-component polyurethane adhesives, in which the technological waiting times until further handling are markedly reduced and the technological floor space requirement and optionally the amount of technological devices needed for this are substantially reduced. Due to the first adhesive layers, which are able to cure rapidly, the components to be joined are fixed in their desired position in relation to one another during joining and such a first bonding strength is reached that immediate further handling of the assembly unit is possible and the joining devices and manufacturing floor space used become free for further assembly units. The property of the first adhesive used according to the present invention, namely, that a defined joining layer thickness is maintained during joining, allows this first adhesive to act as a spacer at the same time. Due to fact that it is applied to selected first bonding surfaces only in a defined layer thickness, larger manufacturing tolerances between the components to be joined can be equalized due to the variable thickness of the second adhesive layer and deviations from the desired shape of the assembly unit can be avoided without difficulty, contrary to the manufacture of such assembly units by welding. At the same time, the risk that the actual layer thickness of the second component will be locally smaller than the minimum layer thickness necessary for optimal strength and the risk that the bonded joints will be filled incompletely due to the components not having been brought sufficiently close to one another are greatly reduced. These risks can be eliminated altogether if the deviations in the shapes of the partners to be joined are measured before joining and the position and/or the layer thickness of the first adhesive is selected corresponding to the result of the measurement.
This process and the use of the adhesives indicated in the exemplary embodiment make it possible in the manufacture of rail-borne vehicles to prepare highly effectively bonded joints in which high elongation at tear and rigidity are combined with a high tolerance to damage and a fatigue strength specific of rail-borne vehicles and the previous complex, stress-transmitting nonpositive and positive-locking connections are equivalent to those needed, e.g., for side wall, front wall and roof sections in the differential design for bodies of rail-borne vehicles, but were hitherto able to be manufactured economically by welding, riveting or screwing only.
A reduction of the joining time can be achieved in a number of applications due to the bonding process according to the present invention compared with joining by means of welding.
This bonding process makes it possible to join components made of different materials into assembly units for bodies of rail-borne vehicles, and differences in the physical behavior (e.g., thermal expansion, elasticity) of the joined components can be equalized by the proper selection of the adhesive.
Compared with the prior-art welding of such assembly units, no deviations in shape due to welding stresses occur during bonding according to the process described, and thermal adjusting operations requiring a high effort are eliminated.
Contrary to the usual welded, riveted or screw connections, joining by bonding does not usually lead to any visual changes on the surfaces of the components or assembly units facing away from the joined surfaces.
Subsequent corrosion protection measures can be carried out much more reliably in bonded connections thus prepared compared with welded assembly units.
The use of this bonding process in rail-borne vehicles makes it possible to manufacture assembly units from components which had already been subjected as blanks or in the course of prefabrication to a special surface treatment (e.g., corrosion protection by galvanization, a decorative lamination with a plastic film or a special protection for the process steps of further processing, e.g., a protective film covering the finished surface of the sheet metal of an outer wall). It is likewise possible to manufacture assembly units in which measures for sound insulation and heat insulation are taken completely already at the stage of the prefabrication (unlike in the case of joining by welding, sparing the areas subjected to thermal stress, which are optionally subjected to an expensive aftertreatment). The process described thus makes possible the manufacture of assembly units that are functionally of a higher quality in conjunction with a higher degree of prefabrication, which saves efforts and costs.
The use of this bonding process substantially increases the freedom of design for shaping the bodies compared with usual welded, riveted or screw connections.
Since the components to be joined by the process according to the present invention may have a design different from that encountered in the case of usual welded, riveted or screw connections, the weight of components and assembly units can be reduced at equal function and strength.
Bonded connections of the type described diminish the generation and above all the transmission of the structure-borne noise, depending on the adhesive used.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.